A jailed Iranian opposition activist and journalist who had been on a hunger strike has died of a heart attack, according to media reports and opposition websites.

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Veteran Iranian opposition activist Hoda Saber was imprisoned in 2009 following the disputed re-election of President Mahmoud Ahmadinejad. ((kalame.com))

News of Hoda Saber's death comes as dissident websites reported a fresh crackdown by police and security forces in Tehran aimed at quelling potential demonstrations on the second anniversary of the disputed re-election of hardline Iranian president Mahmoud Ahmadinejad.

Opposition website kaleme.com said police wielding clubs tried to disperse protesters in one location of the capital, but there were few details.

Saber was reportedly taken to a hospital from Tehran's notorious Evin prison on Friday and died late Saturday, according to the reports.

The veteran activist, in his 50s, had been held at prison since a wave of demonstrations gripped the country two years ago in the wake of the disputed vote, which opposition groups allege was rigged.

Kaleme.com reported that Saber's death was triggered by the hunger strike and prison officials delaying his transfer to a nearby hospital for several hours.

Saber launched the hunger strike 10 days ago in protest of the contentious death of another opposition supporter, Haleh Sahabi, who died after a clash with security forces at her father's funeral earlier this month.

Sahabi herself had been released from prison to attend the funeral of Ezatollah Sahabi, a leading dissident figure and head of the Nationalist Religious Coalition who died of a stroke.

Opposition websites said she died after plainclothes security forces pushed her to the ground during scuffles at the funeral, although the Iranian regime insists she died of a cardiac arrest brought on by natural causes.

The U.S. State Department condemned Sahabi's death and said it was the result of "reprehensible actions" by Iranian security forces.

With files from The Associated Press